Without limiting the scope of the invention, its background is described in connection with the different displacer piston designs for Stirling engines and related devices.
U.S. Pat. No. 4,458,489 issued to Walsh (the '489 patent) describes a new and improved resonant free-piston Stirling engine and method of operation employing a novel virtual rod displacer. According to the '489 patent a rod is secured to and reciprocally moves with the displacer within the Stirling engine and has a rod piston area formed on the end of the rod remote from the displacer with the rod piston area also being subjected to the working gas periodic pressure wave. Suitable support bearings are designed within the Stirling engine housing for reciprocatingly supporting the displacer and rod assembly within the Stirling engine with a set of opposed acting gas springs being provided to act on the displacer end and rod assembly area end of the displacer and rod assembly. One end of the displacer is designed to have a greater effective area acted upon by the gas contained within the engine than the effective area of the opposite end whereby the unbalanced areas of the opposing displacer ends create a differential force when acted upon by a periodic pressure wave, causing reciprocating motion of the displacer and virtual rod assembly. In the preferred embodiment a displacer electrodynamic machine is provided for selectively driving or loading the displacer and rod assembly to thereby control the stroke and/or phase angle at which the displacer and rod assembly move relative to the output power piston or work member.
United States Patent Application No. 20070193266 (McConaghy, 2007) describes a Stirling engine machine comprises a plurality of opposing pairs of cylinder modules. Each cylinder module comprises a first end, a second end, and a piston moveable along a longitudinal axis extending between the first and second ends. The opposing pairs of cylinder modules have axes that are substantially aligned with each other such that movement of the pistons of opposing pairs substantially dynamically cancel. The opposing pairs of cylinder modules have first ends that are in proximity to each other.
United States Patent Application No. 20040194461 (Yamamato, 2003) discloses a Stirling engine comprising: a displacer unit having displacer cylinders, displacers slidably arranged in the chambers of the displacer cylinders, expansion chambers and contraction chambers into which, and from which, the operation gas flows with the operation of the displacers; and a power piston unit having a power cylinder having an operation chamber communicated with either the expansion chamber or the contraction chamber of the displacer unit, and a power piston slidably arranged in the power cylinder; wherein the displacer cylinders of the displacer unit are equipped with a heating wall surrounding a heat source and cooling walls forming a plurality of cylinder chambers surrounding the heating wall; and the displacers of the displacer unit are slidably arranged in the plurality of cylinder chambers in the directions to approach the heat source and to separate away from the heat source.